From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 17346399031 for ; Fri, 26 Jun 2026 20:33:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782506007; cv=none; b=T34mS8RzkiRqsTULk/dOwJR+8NrTZe0e4KXNWclLTeW6/IBHOqpNGsQB25kJc4bQLKSGFeeZMF4AijHwvKi1kGCC2PO+ggOF3nxXpkJRvtNzcM48gLAb+9tfuStUyHF3gyHef+CmRI+fXMi5sfRXeuQlmz+VVzVr6rFMuY56QXw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782506007; c=relaxed/simple; bh=H8kYopqowQBFg4SjwmMA/IPpZdfPVynogmSQo+XU460=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=HqLEEKf+zMQ5zGDxGubHua2dNlSZwMzqboAtz5MZss+mdkRlyO8VWpeQMWwmnoQFm3s6Zo+wo4sFY4avEbU+JJLtxG3H4krygcZXJExV7wfo8bUCOU9sp2//pSAwbUcGKCS+uRY32bbl7A96rCztOt4tWxXuzo06QRSPug/vHH0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=OW/VYPnB; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="OW/VYPnB" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A9EED1F000E9; Fri, 26 Jun 2026 20:33:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782506005; bh=so7ATgFGu/s7mYNzZJ+5Ol8L7q0igIYtf2J+vvbHPLo=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=OW/VYPnBPxPaW41CLCOBkDGD9vSstX/l5cZ+CC5yWBti3j3hRxBdzcSY42pP1k9nC feLz+ls9IAVRZ1NZDntQw1xJ7ndrwY/Px84uSmBeRF+QTTR4gXkDIh5s3ETXvySBMp s8lnG9pu2R6JR1W1v5B4qztvFVFxRncg8Y4QQGwpVSe1DYUtHsWPTySCGd9Pi5rK5E xm+I/Ky1RGS7Q2j/4Vfx64uOoLC5EpPrwlYc3C9SOIVxuPSjpTGlzNjp3wbwIIWl+u R5CDaKvIvRlvPV77kesQUg7XrxMw23lg4b8lmijRUncxrOBjvFzO9U/wrgaMuI5pFa HaT6KaZL/04jg== Message-ID: <05538f68-c3ec-422d-babb-7427068f79f4@kernel.org> Date: Fri, 26 Jun 2026 22:33:19 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 0/3] mm: __access_remote_vm with per-VMA lock To: Rik van Riel , linux-kernel@vger.kernel.org Cc: x86@kernel.org, linux-mm@kvack.org, Thomas Gleixner , Ingo Molnar , Dmitry Ilvokhin , Borislav Petkov , Dave Hansen , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Suren Baghdasaryan , kernel-team@meta.com References: <20260625015053.2445008-1-riel@surriel.com> <5a4ff628c1b947f9cd4da53e1e64b3934a1f2d9a.camel@surriel.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <5a4ff628c1b947f9cd4da53e1e64b3934a1f2d9a.camel@surriel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 6/25/26 13:22, Rik van Riel wrote: > On Thu, 2026-06-25 at 08:32 +0200, David Hildenbrand (Arm) wrote: >> On 6/25/26 03:50, Rik van Riel wrote: >>> >>> v2: >>>  - simplify the code, which should be ok because these copies are < >>> PAGE_SIZE >>>  - clean up the code >>>  - fix locking wrt tlb_remove_table_sync_one() >>>  - hopefully address all the other comments >> >> You mean, ignoring my comments about not reiplementing GUP entirely? >> >> NAK > > Do we actually have a path to doing that? Well, I know what we do not want to reimplement GUP in some GUP users unless really unavoidable. And I want that explored first before moving further into this growing complexity in a GUP users. > > I misread that as more of a wish list thing, not > as something we could realistically do today. I really don't know how you concluded that. I mean, I know, my English is bad, but it's hard for me to get how "Yeah, we're not doing that unless inevitable." is a wish list. Yeah, well, ok, my kids treat also a "no" as a wish list ;) > > How would I go about making that mmap_lock-less > GUP a reality? > > What are the prerequisites? Did you actually read at least some of the stuff I wrote in my mails? You know, the ones where you didn't reply to? :) Seeing a v2 with some weird gup-fast-like looking reimplementatiom (eww) is not something I enjoyed at this point. We don't need another set of special page table walkers. We really need someone to look into this with some GUP experience or the willingness to properly think the GUP lookup+fault path through, instead of adding some creative workarounds to selective GUP user. I will try to find some time to think it through, but my time would be better spent guiding someone (and definitely not someones LLM) to understand (1) which interface we could start with (as I said, a GUP interface where we pass a VMA-lcoked / mm-read-lcoked VMA instead of the MM) (2) which faults we could automatically resolve under VMA lock (I mentioned userfaultfd is tricky but the existing GUP call already doesn't trigger uffd) (3) whether gup-fast could be reused to some degree, or what it would take in order to do that. -- Cheers, David